Plastic discs having a pit optical track structure are well known as compact discs. The term compact disc as used in this application includes any disc shaped recorded medium having pits and lands forming an optical track structure on a data information recording planar surface. Thus it includes such discs where the information stored as pits and lands is digital information, analog information, or information of a graphic or holographic nature. Examples of the different types of information storage are as follows: Digital information may be encoded into the pits and lands as pits of quantized lengths interpretable as a stream of digital data, wherein the length of each pit or land segment may be, for example, related to the number of 1's or 0's in a data stream. An example of such a system is the compact disc ("CD") audio or video disc. Analog information may be encoded into the pits and lands as pit lengths that may vary over a continuum of values, wherein the length of each pit or land segment may be, for example, related to a voltage level in a desired output. An example of such a system is the laser disc video recording system. Graphics may be placed on the surface of a disc by employing the light reflection properties of pitted surfaces that are visible to the unaided eye. Similarly holographic information may be stored in a pit/land format, particularly where it is possible to vary the pit depth to create reflection interference patterns that are visible as a holographic image viewable by the unaided eye.
In-line manufacturing systems are utilized for mass producing copies of compact discs. These systems are capable of producing a compact disc every few seconds once a master disc has been produced. The process employs injection molding, electroplating and printing stages.
Manufacture of high density optical discs is well known. This process however normally requires extreme cleanliness in certain operations to prevent defects in the form of scratches, scuffs, dirt, etc. from gathering on the playside of the disc. Such defects represent at a minimum an inferior cosmetic appearance to the disc and quite possibly a functional problem such as a skip or some other audio/video artifact.